First let me say that I discovered this by accident, and I would never do it on purpose. Well. Maybe I discovered it by a Freudian Slip, so perhaps I already did it on purpose.
Suppose you need to send an email to A, copying B, C and D about something you’d rather hadn’t happened. You particularly wish you didn’t have to bring it to C’s attention, but for this sort of thing you’re expected to email C. So, you misspell C’s email address just a little tiny bit, and send the email. Unless A, B and D look closely, they’ll assume you did the right thing. And maybe C will never hear about it.